The accumulation of chemical waste has become a major health and environmental problem, and numerous legislation such as the Resource Conservation and Recovery Act (RCRA) has already been passed to deal with it. One of the industries that is severely impacted by this legislation is the metalworking industry. Metalworking includes drilling, turning, drawing, forming, sawing, grinding, milling, tapping, threading, honing, broaching, and numerous other machining operations carried out during the manufacture of metal parts, equipment, and artifacts. These processes are highly dependent on proper lubrication and cooling, both of the tool and of the piece of metal on which the operation is carried out ("the workpiece"), and thousands of fluids, both water-based and oil-based, have been developed to meet these needs. Metalworking now includes operations such as the electric discharge machines, which employ petroleum-based fluids (EDM fluids) as cooling and insulating media. Exact estimates vary, but at the time of the filing of this application, the consumption of metalworking fluids is believed to be in excess of three billion gallons per year.
Inevitably, contamination of metalworking fluids will occur, eventually reaching a point where the fluid will no longer be capable of performing its function of cooling and lubricating and may actually be causing corrosion, plugging of lines, and other problems. This contamination occurs from many sources. Metal "fines" and debris from the tools and grinding wheels can accumulate as an abrasive sludge in both oil and water-based fluids. Lubricating oils, way lubricants, and hydraulic fluids from the machinery ("tramp oils") will always find their way into water-based fluids; and, conversely, moisture will usually find its way into oil-based products. Microorganisms present a special problem. Bacteria such as pseudomonas species and Fungi such as Candida species can flourish in oil-water mixtures such as a water-based metalworking fluid contaminated with tramp oils. The result is sludge and deposits, offensive odors, the formation of corrosive acids, and destruction of essential additives necessary for proper fluid performance. Such techniques as filtration of metal fines, the skimming or suctioning off of tramp oil, and the addition of biocides traditionally been used to prolong the life of metalworking fluids. But eventually the fluid will become contaminated to the point where such measures are no longer effective, and at this point in the past the fluid was changed out and disposed of.
Disposal of used and contaminated metalworking fluids, however, is no longer simple and has become very expensive. As recently as ten years ago, said fluids could be trucked to a convenient dumpsite at minimal cost. This is no longer the case. Under RCRA and other legislation, most contaminated metalworking fluid is classified as a hazardous waste which can only be disposed of in a few specially selected dumpsites, which are often located many miles from the plant where the waste was generated. Scrupulous record-keeping must be maintained on such wastes and expensive chemical analyses on each shipment are often required. There are transportation costs, dumping fees, taxes, and miscellaneous additional expenses, to the point that it is now more expensive to dispose of a gallon of metalworking fluid than it originally was to purchase it. But this situation, serious as it is today, will grow even worse, inasmuch as recently enacted legislation calls for the elimination of all chemical waste dumping within four years. When that legislation has gone into effect, the metalworking industry could be faced with billions of gallons of contaminated fluids for which no satisfactory means of disposal will exist. Even now, numerous plants are faced with the necessity of dealing with considerable quantities of contaminated fluids which have been gradually accumulating on the plant site and now must be disposed of in a safe and legal manner.
An obvious alternative to the dumping of used metalworking fluids is that of recycling. Recycling of used crankcase motor oils and other lubricants has been carried out for many years and has received increasing emphasis in view of the energy crisis. However the problems in recycling metalworking fluids are complicated by the bewildering variety of said fluids that exist in the marketplace. There are three basic types of fluid; cutting oils, soluble oils, and synthetics. Cutting oils are petroleum oils used neat or compounded with additives to assist lubrication, protect against corrosion, help wet the metal surface, and so on. They may be of many different viscosities, depending on the metal being machined and the type of machining operation. EDM fluids, while not properly classed as cutting oils, are similar in that they are usually neat petroleum oils (of low viscosity). Soluble oils (or more accurately, emulsifiable oils) are petroleum oils containing emulsifiers and are used in the form of dilute emulsions (usually 5 to 10% soluble oil in water). They combine the lubricating abilities of an oil with the better cooling capabilities of water, and traditionally they have been the most popular type of metalworking fluid. However there is increasing interest in synthetics, which are water-based lubricants which contain no petroleum oil but rely for their lubricating abilities on water-soluble additives such as the polyalkylene glycols. Like soluble oils, synthetics are normally diluted further with water in use. Both the soluble oils and the synthetics may contain supplemental additives such as rust inhibitors, extreme pressure additives, antifoam agents, and biocides, as is well known in the art. Several different fluids may be in use in a given plant at the same time, and the degree of contamination may vary from fluid to fluid and from machine to machine. Thus the problem is one of developing a recycling process that can be used on a multiplicity of contaminated fluids, including soluble oils and synthetics at different concentrations in water and oil-based fluids of differing viscosities. It should be further noted that there may be differences in composition and contamination in a single storage tank or reservoir of used fluid. For example, in an ordinary cyclindrical tank, a contaminated soluble oil containing metal fines, tramp oil, and bacterial sludge will naturally tend to stratify on standing, with the metal settling to the bottom, the oil floating on top, and the bacterial sludge collecting in an interfacial emulsion between the oil and the water. It would be impractical or at the least cumbersome to re-mix the contents of such a tank before recycling, and so inherent in the process itself must be the ability to handle differences in composition encountered as the contaminated fluid is withdrawn from storage into the recycling unit.
In summary, there is an urgent need for a means and process capable of carrying out recycling on a wide variety of water- and oil-based metalworking fluids. There is a further need for a process and means capable of adjusting quickly to differences in fluids or to differences in the composition of the same fluid. There is a further need for a process and means of recycling contaminated metalworking fluids that will be mobile and capable of being used at different plants or different locations within the same plant. The process and means of my invention satisfy these objects.